Scientists at IASF-Palermo study gamma-ray bursts, active galactic nuclei, isolated pulsars, X-ray binaries, high energy cosmic rays.
Gamma-ray Bursts (GRBs) are short-lived and luminous flashes of gamma-rays from space. They can last from a few milliseconds to several minutes and come from random directions of the sky. They originate from sources at cosmological distance, and if they were isotropic emitters their large observed gamma-ray fluences would make them the most luminous objects in the sky. However, there are evidences to believe they are narrowly beamed making them comparable to supernovae in the total energy release.
Read more about the Neil Gehrels Swift Observatory.
Read more about HERMES.
Active galactic nuclei (AGN) are astronomical objects characterized by very high luminosities concentrated in small volumes. This emission is extended over the whole electromagnetic spectrum, from the radio domain through X and gamma-rays. The most probable explanation for their emission is the accretion of matter onto a Super-Massive Black Hole (SMBH), and possibly also the SMBH rotational energy. AGN are a natural laboratory for extreme physics conditions, which cannot be reproduced on Earth. Moreover, their high intrinsic luminosity makes them the most distant observable objects, of great importance for the study of large scale structures in Cosmology.
Isolated Pulsars are neutron stars with strong magnetic fields which emit on a narrow beam along their magnetic axis. The magnetic axis is inclined respect to the rotational axis and the pulsar acts like a lighthouse becoming visible when the beam intersect the line of view. The emission, that is produced at expenses of the rotational energy, is modulated with the star rotation period. The first pulsar was discovered in 1968 in the radio wavelengths and, since then, the number of known radio pulsar has increased considerably. The origin of X-ray emission from this sources is attributed either to thermal and non-thermal process. Thermal emission is characterized by two components at different temperatures. The first component, with a temperature lower than 100 eV, originates from the cooling of stellar surface. The second one is produced in the polar cap regions, two regions around the magnetic axis, heated by accelerated particles that move towards the stellar surface. Its characteristic temperature is about 100-500 eV. The pulsar non thermal emission originates from charge particles accelerated in magnetospheric regions where strong electric fields are present. The location of these regions, called gaps, is not clear. Two classes of models exist at the moment: polar-cap models, with their evolution in the slot gap model, where the acceleration and radiation occur near the stellar surface, and outer-gap models where these processes occur in the outer magnetosphere.
High Mass X-ray Binaries
X-ray binaries are a class of binary stars luminous in X-rays. The emission comes from the accretion of one compact star with matter falling from the companion, usually a normal star. If the normal stellar component has a mass greater than 10 solar masses, the system is known as a high-mass X-ray binary.
Supergiant Fast X-ray Transients are a class of high mass X-ray Binaries (HMXBs) associated with OB supergiants and characterized by show short flares (a few hours, as observed with INTEGRAL). These sources display short, sporadic and bright flares and together with their quiescent level make Supergiant Fast X-ray Transients a class of transients with a large dynamic range.
Ultra-high Energy Cosmic Rays
Ultra-high energy cosmic rays (UHECRs) are extremely energetic subatomic particles (mostly protons, but also some heavier atomic nuclei) coming from the space. It is possible to observe them only indirectly through the cosmic ray showers produced as they interact with the Earth’s atmosphere.
Their source is still a mystery, as does the mechanism to accelerate them to these energies. Possible sources include active galactic nuclei, dormant quasars with associated supermassive black holes and galaxy mergers.
Present and past experiments in this field with IASF-Palermo participation are: JEM-EUSO, Auger and Argo-YBJ.
Read more about JEM-EUSO.
Read more about Auger.
Read more about Argo-JBY.
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